Dienophilie des olefines captodatives : Cycloadditlons de diels-alder de l'α-methylthio-acrylonitrlle et transformation des adduits

The cycloaddition reactions of the α-methylthio-acrylonitrile with 1,3-dienes are investigated. The uncatalysed thermal reactions proceed in high yields very stereoselectively with cyclic dienes and especially even at room temperature with cyclopentadiene. In this later case we shown that the stereoselectivity decreases with increasing temperature. With acyclic dienes the reactions are regio and stereoselective. These both selectivities can be enhanced by Lewis acid catalysis. The stereochemical assignments of the adducts are performed on the basis of spectroscopie data. Then, the cycloadducts are transformed to cyclic (or polycyclic) dienic compounds by sequential oxydation and elimination reactions. Thus, the α-methylthio-acrylonitrile can be considered as an efficient cyano-acetylene equivalent for Diels-Alder reactions.     

Reactivite des fluorovinylsilanespreparation de cetones α-fluorees

Several α-fluoro ketones have been prepared from difluorovinylsilanes inacidic medium.     

Étude des effets de frottement sur la dynamique des ondes de densité de charge dans les systèmes unidimensionnels

In this work, we present the numerical simulation results of the dynamics of charge density waves in one-dimensional systems. With a classical model, we show that the threshold field depends on the friction coefficient of the system. From the threshold field variation versus impurities concentration, we show the existence of three different pinning regimes and we prove that the pinning regime in witch E_c ∝ n_i^4/3 is an intermediate regime between the weak pinning and the strong pinning one, in the sense of Fukuyama, Lee, Rice. We show also that the transition from one pinning regime to the other is continuous.     

Pouvoir de refroidissement des solutions de trempe à base de polymères hydrosolubles

Cooling power of quenchants based on water-soluble polymers. The effects of the concentration of the polymer quenchant, the bath temperature, and agitation on the cooling power of water-based solutions of polyethylene glycol at different molecular weights (PEG-3000, PEG-6000 and PEG-10000) have been investigated. The quenching characteristics of these aqueous polymer quenchant solutions have been determined by means of the cooling curves: T(°C) = f(t), and of the cooling rate curves: T(°C) = f(rate), during the quenching of a cylindrical test probe, made of Inconel 600 (ISO/DIS 9950) in an adequate quench bath. The results have shown that the cooling power increases with agitation, but decreases with increasing temperatures and polymer solutions' concentrations. The variation of these experimental parameters affects significantly the three quenching mechanism steps (vapour blanket, boiling, and convection step).     

Modélisation des temps de réponse des capteurs chimiques

Modelling consists of considering the response and recovery times of a sensor to the target chemical species, as the sum of an ‘intrinsic’ response/recovery time, independent of the experimental conditions, and of an ‘extrinsic’ one, linked to the volume of the measurement cell and to the fluid flow. The experimental response/recovery times being almost always dominated by the extrinsic part, a dissymmetry between the response and recovery signals is observed for sensors whose response is not linear with the concentration of the target chemical species.     

Séparation et dosage de traces de sodium contenues dans des sels de potassium

Résumé Pour séparer et doser les traces de sodium dans les sels de potassium, l'auteur fait appel à deux techniques relativement récentes: la chromatographie sur échangeurs d'ions, la photométrie de flamme.La chromatographie permet de se trouver dans des conditions idéales pour la photométrie de flamme (un seul cation, un seul anion).Il est possible, en s'entourant de précautions indispensables, de doser 0,001% de sodium à ± 10%, grâce à la sensibilité de la photométrie de flamme, et ceci, malgré l'extrême simplicité de l'appareil utilisé.

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Summary To separate and determine traces of sodium in potassium salts, the author used two relatively recent techniques: chromatography on ion exchangers, and flame photometry.The chromatography made it possible to discover ideal conditions for the flame photometry (a single cation, one anion).It is possible, by providing certain indispensable precautions, to determine 0.001% of sodium within ± 10%, thanks to the sensitivity of the flame photometry, and even so, despite the extreme simplicity of the apparatus required.

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Zusammenfassung Zur Trennung und Bestimmung von Natriumspuren in Kaliumsalzen werden die Ionenaustauschchromatographie und die Flammenphotometrie verwendet. Die Chromatographie ermöglicht die Einhaltung der für die Flammenphotometrie bestgeeigneten Bedingungen: je ein Kation und ein Anion. Bei Beachtung der angegebenen Arbeitsvorschriften läßt sich dank der Empfindlichkeit der Flammenphotometrie trotz größter Einfachheit der verwendeten Geräte 0,001% Natrium mit einer Genauigkeit von ±10% bestimmen.

     

Étude numérique de la stabilité des écoulements de convection naturelle dans des espaces annulaires horizontaux de faible épaisseur

The mechanisms driving the multiplicity of multicellular natural convective flows found at the top of narrow horizontal air-filled concentric annuli (the inner cylinder temperature exceeding the outer) are considered. For radius ratio less than R = 1.20, the base flow undergoes an imperfect bifurcation. The two stable branches are characterised.     

Viscoplasticité dynamique du polycarbonate: Influence de la vitesse de sollicitation et des traitements de recuit

The present paper deals with the study of engineering polycarbonates, investigated at high compressive strain rates (1100–3200 sec⁻¹), by means of Hopkinson pressure bar apparatus. Special attention was devoted to the influence of thermal pre-treatment and the viscoelastic behaviour in the glassy state. The results are compared to those obtained at low strain rates (10⁻²−1 sec⁻¹).     

Introduction a l'étude des sels basiques insolubles: Étude des courbes de précipitation des sels basiques insolubles. Produits de solubilité des sels basiques et des hydroxydes

A critical study of curves of precipitation of basic salts by alkali hydroxides shows that the irregularities observed on these curves do not always permit the deduction of the constitution of the salt. They indicate nevertheless the appearance of a new phase and this observation explains, in particular, the important number of wrongly defined basic salts which have been observed.The theory of the titre curves leads to the proposal of formulas permitting the calculation of solubility products of basic salts and even those of hydroxides which were determined very accurately by other methods.     

Prévision des courbes de dosage par potentiométrie bimétallique au moyen des courbes de polarisation

The knowledge of polarisation curves permits the interpretation and prediction of the form of the curves obtained by bimetallic potentiometric determination.     

Méthode de détermination des épaisseurs de films conducteurs par mesures de résistance de surface

To evaluate the thickness of the layers of a Ti/TiAl₃/Al system, experiments based on surface resistance measurements have been performed. The thickness of each layer is deduced from a comparison among calculated and measured values of resistance. We present here a solution for the simulation of surface resistance and the results obtained with this method on Ti/TiAl₃/Al systems.     

Les α et β-Cetophosphonates,des Precurseurs de Pyrrolidines et de Quinoleines Phosphonatees

The condensation of primary amines on α- or β-ketophosphonates affords the corresponding iminophosphonates. The reaction was found to be highly stereoselective, affording the E isomer exclusively. These phosphonylimines were then treated in basic media to give pyrrolidines and quinolines through intramolecular cyclization. The structures of all obtained products were confirmed by NMR spectroscopy (¹H, ³¹P, ¹³C), and in some cases by mass spectrometry.     

Interprétation des mesures potentiométriques au moyen des courbes de polarisation

The observed experimental results of the potentiometric determinations can be explained by means of the polarisation curves. Thus explanations are given of the following phenomena: Electro-activity and non-electro-activity of ions. Nature of the potential taken by an electrode. Time required to establish a stable potential. Significance of the limiting potentials and the limiting concentrations. Influence of oxygen on the value of the measured potentials and on the limit of electro-activity of the oxidants. Significance of the “irreversible” potentials. Formulas giving the potentials in the presence of oxygen. Utility of removing the oxygen from the solution in view of potentiometric determinations. It appears that for all the “slow” redox systems, which are very numerous in inorganic and organic chemistry, the knowledge of the polarisation curves is fundamental.     

Autohésion des élastomères : Anomalie de comportement de l'EPDM

The mechanisms responsible for the anomalous adhesive behaviour of EPDM elastomer have been elucidated by studying the interfacial strength of two EPDM networks. An extremely slow diffusion could be observed and was attributed to the presence of the branching of EPDM macromolecules associated with a high degree of entanglements. It was shown that diffusion is an essential preliminary step to obtain good interfacial co-crosslinking and hence high final adhesive strength.     

Étude par spectrographie infrarouge de la structure de l'acide iodique,de l'acide anhydroiodique et des polyiodates alcalins

Résumé L'étude par spectrographie infrarouge entre 2 et 33 des divers produits de déshydratation de l'acide iodique et des nombreux iodates «acides» et «pyroiodates» qu'il donne avec les iodates alcalins montre l'existence de ponts I-O-I analogues à ceux qui existent dans l'anhydride iodique I₂O₅. Ces liaisons se caractérisent dans la région explorée par deux groupes de bandes fortes à 400–460 cm^–1 et à 515–646 cm^–1, c'est-à-dire en dehors des régions d'absorption caractéristiques des groupements IO₂ ou IO₃.

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Summary The infrared spectrographic study between 2 and 33, of various products of dehydration of iodic acid and numerous acid iodates and pyroiodates which it yields with alkaline iodates reveals the existence of I-O-I bridges analogous to those in I₂O₅. In the regions explored, these links are characterized by two groups of strong bands at 400–460 cm^–1 and at 515–646 cm^–1, i. e. beyond the absorption regions characteristic of the IO₂ or IO₃ groups.

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Zusammenfassung Die IR-spektrographische Untersuchung verschiedener durch Wasserabspaltung aus Jodsäure hergestellter Produkte, zahlreicher saurer Salze und mit Alkalijodaten gebildeter Pyrojodate zwischen 2 und 33 zeigt das Vorhandensein von J-O-J-Brücken, wie sie analog im Jodsäureanhydrid J₂O₅ vorliegen. Charakteristisch für diese Bindung sind im untersuchten Bereich zwei starke Bandengruppen bei 400 bis 460 cm^–1 und bei 515 bis 646 cm^–1, das heißt jenseits des Bereiches der charakteristischen Absorption der Atomgruppen JO2 oder JO3.

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En l'honneur du ProfesseurF. Feigl, pour son 70^e anniversaire.     

La théorie exacte de la flexion des plaques

A new approach is introduced for the analysis and computation of homogeneous, isotropic elastic plates subjected to any bending loads. This approach is based upon a partitioning, which is independent of thickness, of the 3D reference solution into both a part with large variation length and localized effects, whose generalized stress-displacement values are zero. The part with large variation length can easily be computed from data as well as from generalized quantities that represent ‘averages’ in the thickness. These generalized quantities coincide with those obtained from the 3D reference solution; they constitute the solution to an ‘exact’ theory of plate bending.     

Prévision des courbes de dosages potentiométriques

The knowledge of polarisation curves can be used to explain the facts observed in the neighbourhood of the equivalent point in the course of potentiometric determinations as well as the anomalies presented by certain determination curves.It is also possible to interpret the role of a “potential mediator” during the determinations of oxido-reduction potentials.